Abstract
We investigated the humic substances of earth worm casts in different vegetation areas (Shiia siebaldii Makino, Pleioblastus linearis Nakai, Pinus luchuensis Mayr and Ardisia quinquegona Blume) in the Okinawa Islands. The study site was located at Yona University Forest, University of the Ryukyu Islands (26°49'N, 128°5'E). Quartz, kaolinite and illite were included in earthworm casts ; it was suggested that earthworms eat them with the soil when they eat fallen leaves. Total carbon contents showed a significant difference among the fallen leaves, earthworm casts and soils in four vegetation areas. There was no significant difference between the contents of humic acid and fulvic acid in earthworm casts and fallen leaves. Since the amount of humic substances (humic and fulvic acids) in earthworm casts was higher than that in soils, it was suggested that the earthworm casts had accumulated humic substances. Humic acid in earthworm casts and fallen leaves indicated Rp type in all four vegetation areas. It is possible that the humic acid of earthworm casts and fallen leaves was similar in character. IR spectra indicated that humic acids from earthworm casts contained a lower proportion of aromatic components and a larger proportion of aliphatic and polysaccharide components.
